Four families separated under the Trump administration's zero-tolerance policy will be reunited this week, Homeland Security Secretary Alejandro Mayorkas said on a call Sunday night.

Why it matters: Reuniting migrant families is one of Biden's biggest immigration-related promises and progress has been slow.

Driving the news: Mayorkas noted that there are "thousands of families that remain to be reunited" and that DHS will continuing to identify families for reunification in the coming weeks and months.

• Michelle Brané, executive director of the Family Reunification Task Force, said that over a thousand families have been identified thus far.
• Mayorkas added that the files the Biden administration inherited from their predecessors had a "significant number of issues" and that officials have been working to verify much of the information in them.

The big picture: Brané stated that the task force is working identify all the cases of separated families and that "most" of the children set to be reunited with their families are in the U.S.

• The ACLU, which had sued over the separation of children, entered into settlement negotiations with the Biden administration, citing the task force's intentions and work to reunify the remaining families.

What they're saying: "This is just the beginning. We continue to work tirelessly to reunite many more children, with their parents in the weeks and months ahead," Mayorkas said.